1. Field of the Invention
This invention relates to an organic electroluminescence element and a light emitting device employing the electroluminescence element.
2. Description Related Art
An organic electroluminescence element or an organic EL element, is an element having a light emitting layer formed of an organic molecular or organic macromolecular material exhibiting electroluminescent properties. It has ideal properties as a display element such as viewability from a wide viewing angle because cf autogenous light emission and superior shock proofness because it is a fully solid state element. For this reason, research and development are progressing in a number of technological fields.
In general, a high response speed is required as the useful properties of light emitting elements. Several reports have been made in connection with the response speed of the organic EL elements.
For example, it is reported that the response speed of organic EL elements is on the order of several microseconds (SDI Japan Display 89' Proceedings, page 760).
It is also reported that the response speed of organic EL elements is related to the capacitance and the inner resistance of the element, and that the response speed of the element is on the order of microseconds (J. Appl. Phys. 65(1989) 3610).
However, the organic EL element cannot be said to be satisfactory in response speed which is slower than the response speed of a light emitting diode of which response speed is on the order of several tens of nanoseconds.
Because of its slow response speed, the organic EL element cannot be used such as a light emitting diode conventionally employed as a light emitting and transmitting element in a photocoupler or a photointerrupter. The EL element can not be used as a light emitting element for light communication for the similar reason.